The present invention relates to the art of arc welding and, more particularly, to welding apparatus having both local and remote control capabilities with respect to adjusting the welding current.
The present invention finds particular utility in connection with TIG welding apparatus and, accordingly, will be illustrated and described in connection with such apparatus. At the same time, as will become apparent hereinafter, the invention is applicable to welding apparatus other than that for TIG welding and wherein it is desired to provide welding current adjustment capability both at the apparatus and at a welding station or site which is remote therefrom.
TIG welding apparatus has been provided heretofore with selectively operable local and remote welding current selecting arrangements each in the form of a potentiometer for outputting a corresponding control signal by which the welding apparatus power supply is adjusted to output a selected welding current. The local potentiometer is adjustable through a control knob on the power supply, and the remote potentiometer is adjustable through a hand or foot operated device at the remote location and is connected to the power supply through a control cable therebetween.
Such prior welding apparatus includes a switch on the power supply having local and remote modes which provide for selecting between local and remote control of the welding current. When the switch is in the local mode, the welding current is determined by the setting of the knob on the power supply. When the switch is in the remote mode, the welding current is determined by the setting of the remote potentiometer. When the switch is in the remote mode, the remote potentiometer is operable to output a control signal by which the welding current is adjustable from minimum current up to a maximum current as determined by the setting of the local potentiometer.
When TIG welding thin workpieces, current control is critical. While apparatus of the foregoing character operates satisfactorily with respect to welding thin workpieces when the operator positions the switch in the remote position, and properly modulates the remote control, operators may forget to change the switch from the local to the remote mode and then proceed to initiate a welding operation through use of the remote potentiometer with the switch in the local mode. With the foregoing apparatus, as soon as the remote control switch is displaced from the off position, the welding current immediately rises to the current level set by the local potentiometer. Accordingly, if the latter setting provides a higher current level than that needed for welding thin workpieces, the workpieces are burned through and, most often, rendered useless thereby. Moreover, the high current can damage the electrode. Such burn through and/or electrode damage is not only undesirable but also expensive both from the standpoint of lost operator time and from the standpoint of damage workpieces and/or electrode replacement cost.